1. Field of the Invention
This invention relates in general to a dispenser cathode of the indirectly heated type such as a metal capillary cathode for electrical discharge devices having a hollow cylindrical head portion which carries a porous emission wafer of refractive material which covers a cathode cartridge which contains an active material supply.
2. Description of the Prior Art
U.S. Pat. No. 3,821,589 and German DE A No. 2,048,224 disclose dispenser cathodes for electrical discharge vessels particularly metal capillary cathodes wherein active substances from an active substance supply migrate toward the cathode surface through fine openings and a porous active substance carrier covering the supply and formed in particular of porous centered refractive metal such as, for example, tungsten and wherein the active material supply is composed particularly of barium oxide which emits barium during operation. Such structures are known from German Pat. No. 1,217,503. Such cathodes are employed, for example, in travelling wave tubes and in sealed disc tubes.
Cathodes for velocity modulated tubes which in particular are designed for use in space should assure optimally high current densities at the lowest possible cathode temperature over long time spans. This problem usually requires the reduction of the electron affinity in the cathodes. Particularly, in metal capillary cathodes, this requirement can be met in that the carrier metal of tungsten in the system of carrier metal tungsten/absorbent barium is replaced by some other suitable metal or in that the absorbent barium is replaced by other elements. The first comprising wherein the variation of the carrier metal has lead to good results. The most favorable emission values have been achieved in metal capillary cathodes whose emission surfaces are vapor deposited with osmium.
So as to assure an optimally low electron affinity over an optimal operating time in such dispenser cathodes, the individual parameters must be precisely examined particularly so as to observe the required operating data so that the required properties of the cathode are not undesirably deteriorated before use.